1. Field of the Invention
The present invention relates to telecommunication systems, and particularly to a system and method for joint compensation of power amplifier's distortion in an orthogonal frequency division multiplexing (OFDM) telecommunication system.
2. Description of the Related Art
Emerging communication systems intensively use orthogonal frequency division multiplexing (OFDM) technique due to its numerous advantages such as high spectral efficiency, robustness to frequency selective fading, etc, which make it very attractive for the majority of communication systems. However, OFDM signals often result in time-domain wave-forms that have peak to average power ratio (PAPR) of up to 10 dB. These amplitude modulated signals are sensitive to the nonlinear distortions caused by the radio frequency (RF) power amplifier (PA) of the RF front-end. Indeed, the PA needs to linearly amplify the amplitude-modulated signals to avoid high error vector magnitude (EVM) and symbol error rate (SER) which will translate into loss of the information. Simultaneously, the power efficiency of the PA needs to be maximized since the amplifier consumes most of the power in the RF front-end. However, power amplifiers have low power efficiency when they are operated in their linear region, and their efficiency increases as they are driven into the nonlinear region close to saturation. Practically, power amplifiers are operated in their nonlinear region for power efficiency considerations. Then, the linearity is restored by means of system level architectures and mainly linearization techniques such as digital predistortion and feedforward implemented at the transmitter side.
Linearization techniques have been widely used to compensate for the PA's nonlinear distortions at the transmitter side. This is mainly motivated by the regulatory spectrum emission mask requirements in the licensed spectrum bands used for cellular communications and TV broadcasting. In fact, all these applications require that the spectrum at the output of the amplifier meets stringent linearity mask in order to avoid interference with adjacent channels. Among the various linearization techniques, digital predistortion is commonly used. It consists of applying a complementary nonlinearity (predistorter) before the non-linear PA such that the cascade of the predistorter and the amplifier behaves as a linear amplification system. Yet there remains the motivation to find a method for a more power efficient operation of digitally predistorted power amplifiers that maintains spectral efficiency by using a low number of pilot carriers.
Thus, a system and method for joint compensation of power amplifier's distortion solving the aforementioned problems is desired.